Video tape recorders or audio recorders perform a tape drive operation by means of a tape drive mechanisms provided therein, but are basically prone to such trouble that, if the tape, while being driven by that drive mechanism, is dislocated in its width-wise direction, the track of the tape results in deviation, making thus inactive the recording/reproducing functions of those recorders. To avoid the trouble, the arrangement of hitherto, conventional tape drive mechanism has been such that the tape guide posts, which allows sliding of a tape upon each of their surfaces, are equipped with a flange in order for the upper end of the tape or the lower end of the same to come in contact with the flange, or in the mechanism of the type having a rotary drum, a lead is formed on the outer surface of the drum, whereby the tape is mechanically limited its running in the width-wise direction and thus the running position of the tape is adjustingly retained within a given normal point. Further, in the past, no particular tape drive mechanism has been proposed, which has a function for positively eliminating a non-nearly or non-uniformly wound state of the tape around a tape reel. This poor tape winding has been forcibly caused into a normal winding state by the use of the flange of tape guide post or lead on the rotary drum.
However, such prior-art arrangement is based on the forcible way to cause the edges of tape (both side edges of tape as viewed width-wise) to coincide with the flanges of the tape guide post or the lead of the rotary drum, so as to mechanically restrict the running path of the tape within the width-wide direction. Consequently, if the tape is badly non-nearly wound upon a cassette reel, if the tape guide post is not disposed exactly in a perpendicular relation with the tape, or if the tape is run out of a normal path excessively in its width-wise direction due to an excessive large tension exerted on the tape, then the tape being run is at its edges subject to a non-rectilinear friction from the foregoing tape guide post flanges or lead of rotary drum, and the tape per se is not run along stably, which creates a jitters, and may give a damage to the tape in a worst case. Those unfavorable aspects will be more serious, if the tape is of a more thin thickness, and possibly the tape may be prevented from running in a worst situation. For the reasons, it has been difficult to reduce the thickness of the tape as well as to increase a memory capacity of the tape.